Various types of microscopes are used in the ophthalmic field to observe an enlarged view of the eye. Examples of the ophthalmic microscopes include slit lamp microscopes, surgical microscopes, and the like. Some ophthalmic microscopes include an imaging device to capture images of the eye and a binocular optical system to provide binocular disparity for stereoscopic vision.
The ophthalmic microscope is used in the observation of both the anterior segment (the cornea, sclera, conjunctiva, etc.) and the posterior segment (the retina, optic nerve, etc.) of the eye. Although, in general, an auxiliary optical member such as a front lens is additionally used to observe the posterior segment of the eye, if the pupil of the subject's eye is constricted or is small, an observation light flux is blocked by the iris, and it is often the case that the binocular observation cannot be performed suitably. This is likely to occur when the stereo angle of the binocular optical system is large. Meanwhile, information on the depth direction is important in particular to observe the anterior eye segment, and it is necessary to obtain an observation image having a three-dimensional appearance. This requires a sufficiently large stereo angle. In consideration of these circumstances, in the typical conventional ophthalmic microscope, a prism is placed in an observation light path to switch the stereo angle (see, for example, Japanese Unexamined Patent Application Publication No. 2008-86435).
However, the mechanism for changing the stereo angle using a prism is very large, which inevitably increases the size of the ophthalmic microscope. Moreover, the conventional ophthalmic microscope is not able to suitably change the stereo angle. For example, in the conventional ophthalmic microscope, the adjustment range of the stereo angle is narrow, and the fine adjustment cannot be performed.